Transmission belt and associated transmission system

ABSTRACT

A transmission belt his provided which has a first elastomeric material, a plurality of longitudinal inserts comprising a first material, a working surface covered by a covering including a second material, and an opposite surface to said working surface. At least one of the first material and the second material is a fibrous metallic material. Advantageously, the transmission belt is a toothed belt.

TECHNICAL FIELD

The present invention relates to a transmission belt comprising afibrous material covering the working surface that includes metallicfibres. In a preferred embodiment, the transmission belt is a toothedbelt.

PRIOR ART

Transmission belts, and especially toothed belts, generally comprise abody made of an elastomeric material, in which a plurality oflongitudinal thread-like durable inserts, also known hereinafter ascords or simply inserts, is buried and a working surface that, in use,transmits the driving force.

Each component of the belt contributes to increase the performance interms of mechanical resistance, in order to decrease the risk of thebelt breaking and to increase the specific transmissible power.

In particular, the cords contribute to ensure the required mechanicalcharacteristics of the belt and make an-essential contribution todetermine the modulus of the belt and, in particular, to ensure stableperformance over time. The cords are generally obtained by twistinghigh-modulus fibres several times.

The cords or inserts are normally treated with suitable compounds toincrease the compatibility of the fibres with the body compoundsurrounding the cords.

It is known that cords are manufactured in many materials based ondifferent fibres, such as, purely by way of example, carbon, aramid, PBOand glass.

The body compound enables connecting the various elements and ensuresthat they contribute to the final performance of the belt in asynergetic manner.

Body compounds are based on one or more elastomeric materials, possiblyenriched with fibres to increase hardness.

Lastly, the transmission belts have a working surface generally coveredby a fibrous material, for example a covering fabric on the belts, whichhas the task of increasing abrasion resistance and thus protects theworking surface of the belt from wear due to rubbing between the sidesand the slopes of the teeth of the belt and the sides and the throats ofthe grooves of the pulley with which the belt interacts.

In addition, the fibrous covering material reduces the coefficient offriction of the working surface, reduces the deformability of the teethand, most of all, reinforces the root of the tooth, thereby avoiding itsbreakage.

However, in recent engines where performance has increasedsignificantly, toothed belts are subjected to high temperatures andthese temperatures result in quicker deterioration of the materialsforming the various components of the belts.

Furthermore, the belts are often used “in oil”, or rather in systems inwhich the belt is inside the crankcase and therefore in direct contactwith oil spray, or even works partially immersed in an oil bath. Inparticular, the materials of transmission belts used “dry”, designed toresist oil only for a short time and at low temperatures, are unable toprevent deterioration of the mechanical characteristics at hightemperatures and can therefore give rise to teeth breaking andconsequently shorten the mean life of the belt.

To avoid these problems, it is currently known to use covering fabrics,especially for toothed belts, for example with a structure constitutedby woven yarns, or rather yarns that extend, in use, in a longitudinaldirection of the belt, including fibres of polyamide or with a compositestructure, each formed by an elastic yarn as the core and a pair ofcomposite yarns wound around the elastic yarn. Each composite yarncomprises a yarn of high thermal and mechanical resistance and at leastone covering yarn wound around the yarn of high thermal and mechanicalresistance. The elastic yarn could be made, for example, ofpolyurethane. The yarn of high thermal and mechanical resistance couldbe made, for example, of para-aromatic polyamide. The covering yarn ismade of an aliphatic polyamide, in particular nylon 66.

However, this solution is disadvantageous as it easily deteriorates andcauses quite a few belt breakages, in particular in high-temperatureconditions and in systems where the belt works continuously in contactwith oil.

Alternative materials are therefore being sought for the production of acovering for transmission belts, in particular toothed belts, whichenables improving the mechanical and wear resistance characteristics ofknown fabrics.

In addition, in the last few years, more stringent emission regulationshave resulted in designing engines that reach increasingly highertemperatures in the engine compartment when running.

The materials currently used for making the coverings comprise simpleyarns in nylon 66. However, the behaviour of these yarns is not optimalat high temperatures, whether the belts are used dry or in air, and evenmore so when used in systems in oil and therefore inside the enginecrankcase.

Covering fabrics are therefore sought that are resistant to the hightemperatures of current-day engines, whether dry or in oil.

In the end, whether used dry or in oil or inside the engine crankcase,belts are subjected to attack by numerous chemical agents. In systemswhere the belt is used in direct contact or partially immersed in oil,the engine oil often contains pollutants such as ethanol, petrol anddiesel fuel, and combustion residues. In particular, pollution frompetrol that mixes with the oil, even in quite high percentages, dilutingthe oil and attacking the materials constituting the belt, is harmful.

For example, in some applications, the oil can contain up to 30% fuel.The percentage of fuel is variable, depending on the running conditionsof the engine, and increases with high load and low engine temperature.

In addition, the modern, so-called green fuels are particularlyaggressive as they contain numerous additives that attack the polyamideyarns of the fabric.

Covering fabrics are therefore sought that are resistant to chemicalagents, especially at the high running temperatures of the engines inuse today with peaks of roughly 150° C. and up to around 170° C.

Producing coverings for conveyor belts comprising metal is alreadyknown.

However, the known coverings in steel are made with single steel wiresof a diameter well above 50 micron, in both weft and warp, and areextremely rigid. These thick wires are therefore suitable for being usedas sheathing for products that must not flex or only flex very slightly.

These fabrics are therefore not used in transmission belts, especiallyin toothed transmission belts.

Using durable inserts made of aramid fibres, for example those marketedwith the Kevlar® or Twaron® trademarks, in belts for high performance interms of transmissible power is also known.

However, as has long been known, aramid fibres have the drawback of verylow dimensional stability over time, and so a belt with durable insertsin aramid fibres undergoes a shortening of its length during storage,with consequent alteration (reduction) of the initial pitch; it istherefore subjected to higher loads and stress during use, whichnormally result in premature wear triggered by the meshing error createdbetween belt and pulley. Moreover, durable inserts made of aramid fibresrequire a particularly complex and expensive adhesion enhancementtreatment to improve the long-term dimensional stability of the durableinsert, which if not carried out accurately can also entail problems inthe step of cutting the belts.

Alternatively, producing inserts in glass is also known, although thisis a fragile material and therefore not particularly resistant tobending.

In the past, durable steel inserts have been produced by twistingseveral wires, each having a diameter of more than 50 micron and withhigh long-term dimensional stability, but having a high specific weightand, in addition, because the depositing of the reinforcement elementtakes place in a helical manner, these durable elements partially stickout from the side edges of the belts during the belt cutting step, withthe risk of injury to operators when fitting the belt.

To avoid this risk it is therefore necessary to proceed with a furtherfinishing step, which contemplates the removal of the cord strands thatstick out due to the cut and the manual sealing of all the edges of thebelt with adhesive in the areas where the strands partially stuck out.This extra finishing step entails significant additional costs, as it iscarried out by hand and must be carried out of every single belt.

Finally, the flexural strength, i.e. the capacity to support the bendingof these steel wires, is particularly modest, for example, with respectto glass. For this reason, they are no longer used nowadays.

SUBJECT OF THE INVENTION

A first object of the present invention is to obtain a transmission beltcomprising a fibrous covering material that covers the working surfaceand which has a simple structure and is resistant to high temperatures,whether dry or in oil.

A second object of the present invention is also to obtain atransmission belt that comprises a fibrous covering material that isresistant to chemical agents, especially the impurities present inengine oil.

A third object of the present invention is to obtain a toothedtransmission belt having an extremely high modulus and very highlong-term stability and that, at the same time, avoids theabove-described problems regarding known durable inserts.

A further object of the present invention is to obtain a transmissionbelt that has a long service life, and which therefore has excellentmechanical and meshing precision characteristics.

In accordance with the present invention, these objects are achieved bya transmission belt according to claim 1.

In accordance with the present invention, a use according to claim 16 isalso provided.

In accordance with the present invention, a transmission systemaccording to claim 17 is also provided.

BRIEF DESCRIPTION OF DRAWINGS

For a better understanding of the present invention, it will now bedescribed with reference to the attached figures, in which:

FIG. 1 is a partial perspective view of a toothed belt according to thepresent invention;

FIG. 2 is a diagram of a first timing control system using a firsttoothed belt according to the present invention;

FIG. 3 is a diagram of second timing control system using a secondtoothed belt according to the present invention; and

FIG. 4 is a diagram of a third timing control system using a thirdtoothed belt according to the present invention.

DESCRIPTION OF INVENTION

FIG. 1 shows a toothed belt, indicated as a whole by reference numeral1. The belt 1 comprises a body 2, including a first elastomeric materialin which a plurality of longitudinal thread-like durable inserts 3 isburied, and toothing 4 composed of a plurality of teeth that, in use,constitute the working surface 5, or rather the surface that meshes witha corresponding pulley of the transmission system.

The toothed belt also comprises a back 7 opposite to the working surface5.

Preferably, the body 2 is made of a compound comprising one or moreelastomeric materials and numerous additives. For convenience, theelastomeric material(s) is/are hereinafter indicated altogether as the“first elastomeric material”.

The body of the belt advantageously comprises an elastomer as the mainelastomer in the first elastomeric material that is chosen from thegroup constituted by natural rubber (NR), polychloroprene (CR),acrylonitrile butadiene (NBR) and associated hydrogenated elastomersknown as hydrogenated acrylonitrile butadiene (HNBR) or zinc salts ofhydrogenated acrylonitrile butadiene seamed with esters of unsaturatedcarboxylic acid, polyisoprene, styrene-butadiene rubbers,ethylene-alpha-olefin elastomers, EPDM, polyurethane, fluoroelastomers,ethylene-acrylic elastomers (AEM), bromobutyls, chlorosulphonatedpolythene (CSM) or chlorosulphonated alkyl, chlorinated polythene,epoxidized natural rubber, SBR, NBR carboxylates, HNBR carboxylates, ACMand mixtures of these compounds.

The “main elastomer” is intended as being present in the compound thatconstitutes the body for more than 50% by weight, calculated on thetotal weight of all the elastomers in the compound and thereforeexcluding all other non-elastomeric components of the belt.

The body preferably comprises at least one copolymer of polyolefin or arubber containing acrylonitrile units as the first or a furtherelastomeric material.

More advantageously, the copolymer(s) used as body compounds are nitrilerubbers, advantageously acrylonitrile butadiene rubbers, known as NBR.Even more advantageously, they are hydrogenated acrylonitrile butadiene,or HNBR, or even XHNBR, i.e. hydrogenated and carboxylated acrylonitrilebutadiene.

Advantageously, the HNBR used for making the transmission systems inwhich the belt is partially in an oil bath or in direct contact with oiland impurities has a high level of hydrogenation, for example so-calledcompletely saturated HNBRs can be used, these having a percentage ofresidual double bonds of 0.9% at most, but HNBRs with a lower level ofunsaturation can also be used in alternative, such as, for example,so-called partially saturated HNBRs having a saturation level of 4% or5.5%.

Some examples of HNBR copolymers that can be used in the body compound,but also in the different treatments of the various elements forming thetoothed belt, include copolymers belonging to the THERBAN family made byLanxess, such as THERBAN 3407 with 34% nitrile groups and ahydrogenation level of 0.9% at most, THERBAN 3406 with 34% nitrilegroups and an unsaturation level of 0.9% at most, THERBAN 3607 with 36%nitrile groups and an unsaturation level of 0.9% at most, THERBAN 3446with 34% nitrile groups and an unsaturation level of 4% at most, THERBAN3447 with 34% nitrile groups and an unsaturation level of 5.5% at most,THERBAN 3627 with 36% nitrile groups and an unsaturation level of 2% atmost, THERBAN 3629 with 36% nitrile groups and an unsaturation level of2% at most, and THERBAN 3907 with 39% nitrile groups and an unsaturationlevel of 0.9% at most.

Alternatively, it is also possible to use HNBRs made by Nippon Zeon withthe name ZETPOL. In particular, ZETPOL 2000 with 36% nitrile groups andan unsaturation level of 0.9% at most, ZETPOL 2000L with 36% nitrilegroups and an unsaturation level of 0.9% at most, ZETPOL 2010 with 36%nitrile groups and an unsaturation level of 4% at most, ZETPOL 2010Lwith 36% nitrile groups and an unsaturation level of 4% at most, ZETPOL2010H with 36% nitrile groups and an unsaturation level of 4% at most,ZETPOL 2020 with 36% nitrile groups and an unsaturation level of 5.5% atmost, and ZETPOL 2020L with 36% nitrile groups and an unsaturation levelof 5.5% at most.

More advantageously, the acrylonitrile units in the elastomer forapplications in oil are between 33% and 51%, for example 50% by weight,while for dry applications they are between 15% and 25% by weight, forexample 21% by weight.

Even more advantageously, a polymer formed by a mixture of one or morecopolymers, obtained starting from a diene monomer and a monomercontaining nitrile groups where an acid or salt of an unsaturatedcarboxylic acid is added to one or more of these copolymers, is used incombination with a first polymer. More advantageously, the unsaturatedcarboxylic acid is methacrylic or acrylic acid and said salt is a zincsalt of methacrylic or acrylic acid. Even more advantageously, a zincsalt of methacrylic acid is used. Even more advantageously, the zincsalt of methacrylic acid is added in a quantity in the range between 10and 60 phr.

For example, the elastomers sold by Zeon under the following names canbe used advantageously: ZSC 1295, ZSC 2095, ZSC 2195, ZSC 2295, ZSC2295L, ZSC 2295R and ZSC 2395.

In particular, it is possible to partially or entirely replace thepreviously mentioned HNBRs, namely ZETPOL and/or THERBAN with a ZSC thatcomprises an unsaturated carboxylic acid and zinc oxide and/or withTHERBAN ART that comprises an unsaturated carboxylic acid salt.

Mixed compounds of polyolefin and rubber containing acrylonitrile unitsare also preferred, more preferably compounds containing a copolymer ofethylene with NBRs or HNBRs or the above-mentioned modified HNBRs. Forexample, rubbers containing EPDM (ethylene-propylene diene monomer) orEPM (ethylene-propylene monomer) can be added to polymers containingacrylonitrile units in quantities preferably in the range between 1% and30%.

In addition to the elastomeric materials, the body compound can compriseconventional additives such as, for example, reinforcement agents,extenders, pigments, stearic acid, accelerators, vulcanization agents,antioxidants, activators, initiators, plasticizers, waxes,prevulcanization inhibitors, antidegradants, process oils and similar.

Advantageously, carbon black can be employed as an extender, beingadvantageously added in quantities in the range between 0 and 80 phr,more advantageously about 40 phr. Advantageously, light-colouredreinforcing extenders such as talc, calcium carbonate, silica andsilicates are added in quantities advantageously in the range between 0and 80 phr, advantageously about 40 phr. It is also possible toadvantageously use silanes in quantities in the range between 0 and 5phr.

Advantageously, zinc and magnesium oxides are added in a quantityranging between 0 and 15 phr.

Advantageously, ester plasticizers such as trimellitates or ethyl estersare added in a quantity advantageously ranging between 0 and 20 phr.

Advantageously, vulcanization coagents such as triallyl cyanurates andorganic or inorganic methacrylates such as metal salts areadvantageously added in a quantity ranging between 0 and 20 phr, ororganic peroxides, such as isopropyl benzene peroxide for example, in aquantity advantageously ranging between 0 and 15 phr.

It is understood that use “in-oil” means that the belt is used partiallyimmersed in an oil bath or in direct contact with oil. In general, inuse, the belt can be inside the engine crankcase, for example, as analternative to chain or gear systems.

It is understood that “dry” use means that the belts are outside theengine crankcase and are only accidentally in contact with engine oiland not generally in contact with oil mixed with petrol.

It is understood that use “in oil mixed with petrol” means that thetoothed belt is used in a mixture of oil with percentages of petrol evenexceeding 30%.

In the following, reference will be made to an example of producing thetransmission belt of the present invention with reference to a toothedbelt, but it is obvious that the transmission belt could also be amulti-groove belt or so-called poly-V belt.

In one aspect of the present invention, the transmission belt comprisesinserts 3, also known as cords or durable inserts, arranged in alongitudinal direction and including a fibrous metallic material.

It is understood that fibrous metallic material means a materialincluding metallic fibres.

It is understood that metallic fibres means composite fibres not onlyjust of metal, but also metal covered by polymeric material or fibres ofa polymeric material covered by metal.

In another aspect of the present invention, the working surface 5 of thetransmission belt is covered with a covering 8 including a fibrousmetallic material.

It is understood that working surface means the face of the belt that,in use, meshes with the pulley and via which the drive is transmitted.Clearly, the working surface can comprise one or more coverings andsubsequent treatments that all contribute to the belt's performance andonly one of them will be effectively on the outside and in contact withthe pulley.

Advantageously, the transmission belt comprises both inserts 3 and thecovering 8 including a fibrous metallic material.

Advantageously, the fibrous metallic material is based on fibres havinga diameter of between 2 and 40 λm.

More advantageously, the fibrous metallic material is based on fibreshaving a diameter of between 5 and 15 μm.

More advantageously, the fibrous metallic material is steel, even moreadvantageously stainless steel.

For example, the fibrous metallic material could be a material chosenfrom those sold under the Naslon registered trademark.

Advantageously, the fibrous metallic material comprises filamentsincluding fibres, more advantageously it comprises yarns includingfilaments including metallic fibres.

Advantageously, the fibrous metallic material comprises complex orhybrid yarns composed of several fibrous materials.

Advantageously, the covering 8 of the working surface 5 is chosen fromthe group constituted by woven fabric, knitted fabric and non-wovenfabric.

In the case where a woven fabric or a knitted fabric is used, the fabricyarns include the fibrous metallic material.

More advantageously, the fibrous metallic material is a fabric.

Advantageously, the fibrous metallic material has a weight of between500 and 1500 g/m2.

More advantageously, the fabric comprises yarns that extendsubstantially in the longitudinal direction of the toothed belt. As arule, these longitudinal yarns are weft yarns.

In the case where the transmission belt is a toothed belt, thelongitudinal yarns including the fibrous metallic material aresubstantially parallel to the inserts 3.

Advantageously, the fabric comprises longitudinal yarns and transverseyarns both including the fibrous metallic material.

Alternatively, the transverse yarns include a material chosen from thegroup constituted by polyamides and polyesters. More advantageously, thetransverse yarns include polyamides, even more advantageously aromaticpolyamides such as para-aramids or meta-aramids for example, e.g.materials sold under the Conex registered trademark.

Advantageously, the longitudinal yarns comprise composite yarns formedby at least two yarns.

More advantageously, the yarns comprise at least one elastic yarn aroundwhich at least one yarn including metallic fibres is wound.

The covering fabric 8 of the toothing 4 can be formed by one or morelayers and can be obtained via different weaving techniques, forexample, preferably twill weaving, even more preferably 2×2 twillweaving.

For example, in a first embodiment of the present invention, thecovering fabric 8 has a structure constituted by longitudinal yarnsforming the weft and transverse yarns forming the warp, in which atleast the weft is constituted by yarns including metallic fibres.

Advantageously, the yarns include metallic fibres for at least 25% byweight and, even more preferably, could be made entirely of metallicfibres.

Optionally, the warp is also constituted by warp yarns includingmetallic fibres.

In a second embodiment of the present invention, the covering fabric 8has a structure constituted by longitudinal yarns forming the weft andtransverse yarns forming the warp, in which at least the weft has acomposite structure, i.e. constituted by weft yarns each formed from anelastic yarn as the core and a pair of composite yarns wound around theelastic yarn; each composite yarn comprises a yarn of high thermal andmechanical resistance and at least one covering yarn wound around theyarn of high thermal and mechanical resistance. The elastic yarn ismade, for example, of polyurethane. The yarn of high thermal andmechanical resistance is made, for example, of para-aromatic polyamide.The covering yarn is made of metallic fibres.

In a third embodiment of the present invention, the covering fabric 8has a structure constituted by longitudinal yarns forming the weft andtransverse yarns forming the warp, in which at least the weft has acomposite structure, i.e. constituted by weft yarns each formed from anelastic yarn as the core around which a yarn of high thermal andmechanical resistance is wound. A covering yarn is subsequently wound onthe yarn of high thermal and mechanical resistance. The elastic yarn ismade, for example, of polyurethane. The yarn of high thermal andmechanical resistance is made, for example, of para-aromatic polyamide.The covering yarn is made of metallic fibres.

According to a preferred embodiment of the present invention, the woven,knitted, or non-woven covering fabric of the working surface 8 of thetransmission belt 1 is treated with at least a first and/or secondprotection or adhesion enhancement treatment.

Advantageously, it is subjected to a first protection or adhesiontreatment, for example, with RFL.

More advantageously, it is also subjected to a second protectiontreatment comprising a second elastomeric material different from or thesame as that forming the body of the belt.

More advantageously, the second protection treatment also comprises ananti-friction material, for example, chosen from the group constitutedby copper powder, molybdenum sulphide, graphite and a fluorinatedhomopolymer or copolymer or mixture thereof.

Even more advantageously, the anti-friction material is PTFE.

Advantageously, one or more copolymers formed from a monomer containingnitrile groups and a diene are used as the second elastomeric material.

Advantageously, the monomers containing nitrile-groups are in apercentage in the range between 15% and 60% with respect to the entiretyof end copolymers.

More advantageously, they are between 15% and 25% by weight for coldapplications with temperatures down to −40° C., between 33% and 39% byweight for belts with dry applications and between 39% and 51% by weightfor in-oil applications.

Even more advantageously, for in-oil applications they are between 34%and 49% by weight, while for dry applications also suitable forlow-temperature starting they are between 19% and 23% by weight, forexample 21% by weight.

More advantageously, the copolymer(s) used are nitrile rubbers,advantageously acrylonitrile butadiene rubbers, known by the acronymNBR. Even more advantageously, they are hydrogenated acrylonitrilebutadiene or HNBR, or even XHNBR, i.e. carboxylated hydrogenatedacrylonitrile butadiene.

By opportunely choosing the quantities of the materials of which it iscomposed, the protection treatment can form a covering coating 9,distinct and separate from the fibrous material, also referred tohereinafter as the wear-resistant coating 9. The wear-resistant coating9 constitutes the working surface of the belt and therefore furtherincreases wear resistance and avoids oil absorption.

Advantageously, PTFE is present in the wear-resistant coating in alarger phr quantity than the second elastomeric material.

The gauge of the wear-resistant coating 9 is advantageously between 0.03mm and 0.2 mm.

The wear-resistant coating 9 can be placed over the covering fabric 8 indifferent ways. Preferably, it is placed by means of a calendering step.

Preferably, to ensure the necessary resistance, the wear-resistantcoating 9 weighs between 50 and 400 gr/m².

Preferably, the back 7 of the belt is also covered by a fibrous coveringmaterial, preferably the same as that previously described.

In one aspect of the present invention, the inserts 3 are formed by aplurality of filaments or yarns and each yarn is formed by a pluralityof filaments.

Advantageously, each insert 3 comprises between 3 and 20 yarns.

Even more advantageously, each insert 3 comprises between 5 and 15 yarnstwisted together. For example, the embodiment in which there are 11yarns proved to be particularly preferred.

More advantageously, each yarn comprises between 50 and 500 filaments.Even more advantageously, between 100 and 300 filaments, for example200.

Even more preferable, each filament is made from metallic fibres havinga diameter of between 10 and 15 micron. For example, the embodiment inwhich the diameter of the single fibres forming the filaments is 12micron proved to be particularly preferred.

In an alternative preferred embodiment of the invention, the inserts 3also comprise a second fibrous material.

The second fibrous material used for producing the inserts 3 ispreferably chosen from a group composed of glass fibres, aramid fibres,polyester fibres, carbon fibres and PBO fibres.

The fibrous metallic material preferably has a higher modulus than thesecond material and the second material is preferably wound around thefibrous metallic material.

The second material is preferably chosen so as to solve problems ofcompatibility with the compound of the surrounding body.

In section, the second material preferably occupies an area of between15% and 75% with respect to the overall surface of the section. Evenmore preferably, the second material occupies an area of between 45% and55% with respect to the overall surface.

Preferably, the inserts according to the present invention have a twistof the Lang's twist type, namely they have two twists in the samedirection, as this this construction has been found to be particularlyeffective.

It is possible to vary the number of filaments or yarns that form adurable insert, as well as the number of base filaments or the count orthe entire construction of the insert without departing from the presentinvention.

Preferably, the fibres forming the cord are treated with HNBR latexvulcanized with water-soluble peroxides by means of the procedureillustrated in patent WO2004057099 in the name of Nippon Glass.

Preferably, the treatment therefore comprises a treatment liquid,preferably an aqueous adhesive and consequently including more than 50%water, comprising elastomeric latex material and a vulcanizationaccelerator.

As a rule, the water portion evaporates during vulcanization and onlythe latex remains on the finished belt.

Preferably, the latex comprises a third elastomeric material includingone or more copolymers formed from a monomer containing nitrile groupsand a diene in which the monomers containing nitrile groups are in apercentage of between 30% and 39% by weight with respect to entirety ofend copolymers. More preferably, the nitrile groups are in a percentageof between 30% and 32% by weight with respect to entirety of endcopolymers.

A transmission belt and, in particular, a toothed transmission belt 1according to the present invention are produced using knownmanufacturing processes.

The transmission belts according to the present invention areparticularly suitable for being used in systems in direct contact withor partially immersed in oil, in particular engine oil at hightemperatures, such as those reached in recently developed engines, forexample even higher than 130°, and inside the vehicle's enginecrankcase. In particular, excellent results have been achieved in thecase where the belt is used as a replacement for traditional gear orchain systems, systems in which the belt is exposed for its entireworking life to continuous contact with oil spray or is possiblypartially immersed in an oil bath.

In this case, when a covering fabric 10 is present on the back, it isquite advantageous to carry out the adhesive treatment and/or theprotection treatment on the back 7 of the transmission belt as well. Inthis case, the treatment enables preventing oil penetration from theback 7 of the toothed belt 1 as well, and is particularly advantageouswhen the toothed belt 1 is used in control systems in which the back 7of the belt is in contact with shoes or tensioners. In fact, in thesesystems oil remains interposed between the contact surface of the shoeor tensioner with the belt and the back of the belt and thereforepenetration inside the mixture that constitutes the body would befavoured.

Preferably, the toothed belt 1 can be treated on all the outsidesurfaces and, in particular, on the sides where the body mixture is mostexposed to attack by oil, with a swelling resistant rubber, for exampleENDURLAST (registered trademark of Lord).

The belt 1 according to the present invention is advantageously used,for example, in a timing control system for a motor vehicle of the typedepicted in FIG. 2. The timing control system is indicated as a whole inthe figure by reference numeral 11 and comprises a drive pulley 12rigidly fastened to the driveshaft, not shown, a first 13 a and a second13 b driven pulley and a tensioner 14 for tensioning the toothed belt.

According to a second alternative embodiment, shown in FIG. 3, a toothedbelt according to the present invention is indicated by referencenumeral 1, this belt having toothing on both faces and therefore acovering 8 on one or both of the toothings.

The timing control system is indicated as a whole in the figure byreference numeral 21 and comprises a drive pulley 22 rigidly fastened tothe driveshaft, not shown, a first 23 a, a second 23 b and a third 24driven pulley.

According to a third embodiment of the present invention, shown in FIG.4, a toothed belt 1 according to the present invention canadvantageously be used in a timing control system indicated as a wholein the figure by reference numeral 31, which comprises a drive pulley 32rigidly fastened to the driveshaft, not shown, a first 33 a and a second33 b driven pulley, a shoe tensioner 34 and a shoe 35.

In particular, the transmission belt of the present invention has provedto be particularly effective when used in a transmission system commonlyreferred to as balance shafts.

In use, the toothed belts 1 in the respective control systems 11, 21 and31 are in direct contact with oil.

FIGS. 2 to 4 refer to control systems related to the movement of balancecountershafts, but it is clear that the belt according to the presentinvention can also be used in so-called cam-to-cam systems or fordriving the oil pump. In these cases, the belt becomes partiallyimmersed in an oil bath during operation.

Furthermore, it is also possible to use the belt of the presentinvention in the main transmission for driving cams and also for drivingthe injection pump in diesel engines.

It has been experimentally verified that the use of the fabric andinserts according to the present invention enables achieving effectiveoil resistance even at high temperatures and consequently enablespassing the endurance tests to which toothed belts are subjected inorder to be used in motor vehicles and therefore avoids all the beltproblems when used in contact with oil and, in particular, the fall-offin mechanical characteristics, less adhesion, worse meshing and lesswear resistance.

Alternatively, the belt according to the present invention can also beused as a dry belt for engine timing.

From examination of the characteristics of the belt produced accordingto the present invention, the advantages that can be achieved with itare evident.

Advantageously, the above-described belts can consequently be used forboth dry and in-oil high-temperature applications, even in the presenceof contaminants, for example green fuels, which are particularlyaggressive.

1. A transmission belt comprising a body including a first elastomericmaterial, a plurality of longitudinal inserts comprising a firstmaterial, a working surface covered by a covering comprising a secondmaterial, and an opposite surface to said working surface, wherein atleast one of said first material and said second material is a fibrousmetallic material comprising fibres with a diameter of between 2 and 40μm.
 2. A transmission belt according to claim 1, wherein said fibrousmetallic material comprises fibres with a diameter of between 5 and 15μm.
 3. A transmission belt according to claim 1, wherein said fibrousmetallic material is steel.
 4. A transmission belt according to claim 1,wherein the second material is chosen from the group constituted bywoven fabric, knitted fabric and non-woven fabric.
 5. A transmissionbelt according to claim 4, wherein said second material is a fabric. 6.A transmission belt according to claim 4, wherein said fibrous metallicmaterial has a weight of between 500 and 1500 g/m².
 7. A transmissionbelt according to claim 4, wherein said fabric comprises yarns thatextend in the longitudinal direction and include said fibrous metallicmaterial.
 8. A transmission belt according to claim 7, wherein saidyarns comprise at least one elastic yarn around which at least one yarncomprising said second material is wound.
 9. A transmission beltaccording to claim 7, wherein said fabric comprises both longitudinalyarns and transverse yarns including said fibrous metallic material. 10.A transmission belt according to claim 1, wherein said first material isa fibrous metallic material based on fibres having a diameter of between2 and 40 μm.
 11. A transmission belt according to claim 1, wherein saidinserts are formed by a plurality of yarns and each yarn is formed by aplurality of filaments.
 12. A transmission belt according to claim 1,wherein each one of said inserts comprises between 3 and 20 yarns.
 13. Atransmission belt according to claim 11, wherein each one of said yarnscomprises between 50 and 500 filaments.
 14. A transmission beltaccording to claim 11, wherein said inserts also comprise a secondfibrous material.
 15. A transmission belt according to claim 1, whereinit is a toothed belt.
 16. (canceled)
 17. A transmission systemcomprising: a transmission belt according to claim
 1. 18. A transmissionsystem for a motor vehicle comprising; at least one drive pulley, adriven pulley, a transmission belt and means for maintaining said beltin direct contact with oil or partially immersed in oil, wherein saidtransmission belt comprises: a body including a first elastomericmaterial, a plurality of longitudinal inserts including a firstmaterial, a working surface covered by a covering including a secondmaterial, and an opposite surface to said working surface, wherein atleast one of said first material and said second material is a fibrousmetallic material comprising fibres with a diameter of between 2 and 40μm.
 19. The transmission system of claim 17, wherein said transmissionbelt is at least partially in an oil bath or continuously in contactwith oil.